Matte finish polyimide films and methods relating thereto

ABSTRACT

The present disclosure is directed to a base film having a thickness from 8 to 152 microns, a 60 degree gloss value from 2 to 35, an optical density greater than or equal to 2 and a dielectric strength greater than 1400 V/mil. The base film comprises a chemically converted (partially or wholly aromatic) polyimide in an amount from 71 to 96 weight percent of the base film. The base film further comprises a pigment and a matting agent. The matting agent is present in an amount from 1.6 to 10 weight percent of the base film, has a median particle size from 1.3 to 10 microns, and has a density from 2 to 4.5 g/cc. The pigment is present in an amount from 2 to 9 weight percent of the base film. The present disclosure is also directed to coverlay films comprising the base film in combination with an adhesive layer.

This application is a continuation of application Ser. No. 12/842,174,filed on Jul. 23, 2010, which claims the benefit of provisionalApplication No. 61/230,934, filed on Aug. 3, 2009, the entiredisclosures of which are incorporated herein by reference thereto.

FIELD OF DISCLOSURE

The present disclosure relates generally to matte finish base films thatare useful in coverlay applications and have advantageous dielectric andoptical properties. More specifically, the matte finish base films ofthe present disclosure comprise a relatively low concentration ofpigment and matting agent in a polyimide film imidized by a chemical (asopposed to a thermal) conversion process.

BACKGROUND OF THE DISCLOSURE

Broadly speaking, coverlays are known as barrier films for protectingelectronic materials, e.g., for protecting flexible printed circuitboards, electronic components, leadframes of integrated circuit packagesand the like. A need exists however, for coverlays to be increasinglythin and low in cost, while not only having acceptable electricalproperties (e.g., dielectric strength), but also having acceptablestructural and optical properties to provide security against unwantedvisual inspection and tampering of the electronic components protectedby the coverlay.

SUMMARY OF THE INVENTION

The present disclosure is directed to a base film. The base filmcomprises a chemically converted polyimide in an amount from 71 to 96weight percent of the base film. The chemically converted polyimide isderived from: i. at least 50 mole percent of an aromatic dianhydride,based upon a total dianhydride content of the polyimide, and ii. atleast 50 mole percent of an aromatic diamine based upon a total diaminecontent of the polyimide. The base film further comprises: a lowconductivity carbon black present in an amount from 2 to 9 weightpercent of the base film; and a matting agent that:

-   -   a. is present in an amount from 1.6 to 10 weight percent of the        base film,    -   b. has a median particle size from 1.3 to 10 microns, and    -   c. has a density from 2 to 4.5 g/cc.        In one embodiment, the base film has: i. a thickness from 8 to        152 microns; ii. a 60 degree gloss value from 2 to 35; iii. an        optical density greater than or equal to 2; and iv. a dielectric        strength greater than 1400 V/mil. The present disclosure is also        directed to coverlay films comprising the base film in        combination with an adhesive layer.

DETAILED DESCRIPTION OF THE INVENTION Definitions

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a method,process, article, or apparatus that comprises a list of elements is notnecessarily limited only to those elements but may include otherelements not expressly listed or inherent to such method, process,article, or apparatus. Further, unless expressly stated to the contrary,“or” refers to an inclusive or and not to an exclusive or. For example,a condition A or B is satisfied by any one of the following: A is true(or present) and B is false (or not present), A is false (or notpresent) and B is true (or present), and both A and B are true (orpresent).

Also, use of the “a” or “an” are employed to describe elements andcomponents of the invention. This is done merely for convenience and togive a general sense of the invention. This description should be readto include one or at least one and the singular also includes the pluralunless it is obvious that it is meant otherwise.

“Dianhydride” as used herein is intended to include precursors orderivatives thereof, which may not technically be a dianhydride butwould nevertheless react with a diamine to form a polyamic acid whichcould in turn be converted into a polyimide.

“Diamine” as used herein is intended to include precursors orderivatives thereof, which may not technically be a diamine but wouldnevertheless react with a dianhydride to form a polyamic acid whichcould in turn be converted into a polyimide.

“Polyamic acid” as used herein is intended to include any polyimideprecursor material derived from a combination of dianhydride and diaminemonomers or functional equivalents thereof and capable of conversion toa polyimide via a chemical conversion process.

“Prepolymer” as used herein is intended to mean a relatively lowmolecular weight polyamic acid solution which is prepared by using astoichiometric excess of diamine in order to give a solution viscosityof approximately 50-100 Poise.

“Chemical conversion” or “chemically converted” as used herein denotesthe use of a catalyst (accelerator) or dehydrating agent (or both) toconvert the polyamic acid to polyimide and is intended to include apartially chemically converted polyimide which is then dried at elevatedtemperatures to a solids level greater than 98%.

“Finishing solution” herein denotes a dianyhdride in a polar aproticsolvent which is added to a prepolymer solution to increase themolecular weight and viscosity. The dianhydride used is typically thesame dianhydride used (or one of the same dianhydrides when more thanone is used) to make the prepolymer.

When an amount, concentration, or other value or parameter is given aseither a range, preferred range or a list of upper preferable values andlower preferable values, this is to be understood as specificallydisclosing all ranges formed from any pair of any upper range limit orpreferred value and any lower range limit or preferred value, regardlessof whether ranges are separately disclosed. Where a range of numericalvalues is recited herein, unless otherwise stated, the range is intendedto include the endpoints thereof, and all integers and fractions withinthe range. It is not intended that the scope of the invention be limitedto the specific values recited when defining a range.

In describing certain polymers it should be understood that sometimesapplicants are referring to the polymers by the monomers used to makethem or the amounts of the monomers used to make them. While such adescription may not include the specific nomenclature used to describethe final polymer or may not contain product-by-process terminology, anysuch reference to monomers and amounts should be interpreted to meanthat the polymer is made from those monomers, unless the contextindicates or implies otherwise.

The materials, methods, and examples herein are illustrative only and,except as specifically stated, are not intended to be limiting. Althoughmethods and materials similar or equivalent to those described hereincan be used in the practice or testing of the present invention,suitable methods and materials are described herein.

Base Film

The base films of the present disclosure comprise a filled polyimidematrix, where the polyimide is created by a chemical conversion process.One advantage of a chemical conversion process (over a solely thermalconversion process) is that the amount of matting agent necessary toachieve sufficient low gloss is at least 10, 20, 30, 40 or 50 percentless than if a thermal conversion process is used. Generally acceptedranges for 60 degree gloss values are:

<10 flat 10-70 matte, satin, semi-gloss (various terms are used) >70glossy.In some embodiments, the base film has a 60 degree gloss value betweenand optionally including any two of the following: 2, 3, 4, 5, 10, 15,20, 25, and 35. In some embodiments, the base film has a 60 degree glossvalue from 2 to 35. In some embodiments, the base film has a 60 degreegloss value from 10 to 35. The 60 degree gloss value is measured usingMicro-TRI-Gloss gloss meter. The lower loading of matting agent (madepossible by the chemical conversion) is advantageous, because it: i.lowers overall cost; ii. simplifies the dispersion of matting agent intothe polyamic acid (or other polyimide precursor material); and iii.provides the resulting base film with better mechanical properties(e.g., less brittleness). Another advantage of a chemical conversionprocess (over a thermal conversion process) is that the dielectricstrength of the chemically converted base films is higher. In someembodiments, the base film dielectric strength is greater than 1400V/mil (55 V/micron).

In a chemical conversion process, the polyamic acid solution is eitherimmersed in or mixed with conversion (imidization) chemicals. In oneembodiment, the conversion chemicals are tertiary amine catalysts(accelerators) and anhydride dehydrating materials. In one embodiment,the anhydride dehydrating material is acetic anhydride, which is oftenused in molar excess relative to the amount of amic acid (amide acid)groups in the polyamic acid, typically about 1.2 to 2.4 moles perequivalent of polyamic acid. In one embodiment, a comparable amount oftertiary amine catalyst is used.

Alternatives to acetic anhydride as the anhydride dehydrating materialinclude: i. other aliphatic anhydrides, such as, propionic, butyric,valeric, and mixtures thereof; ii. anhydrides of aromatic monocarboxylicacids; iii. Mixtures of aliphatic and aromatic anhydrides; iv.carbodimides; and v. aliphatic ketenes (ketenes may be regarded asanhydrides of carboxylic acids derived from drastic dehydration of theacids).

In one embodiment, the tertiary amine catalysts are pyridine andbeta-picoline and are typically used in amounts similar to the moles ofanhydride dehydrating material. Lower or higher amounts may be useddepending on the desired conversion rate and the catalyst used. Tertiaryamines having approximately the same activity as the pyridine, andbeta-picoline may also be used. These include alpha picoline;3,4-lutidine; 3,5-lutidine; 4-methylpyridine; 4-isopropyl pyridine;N,N-dimethylbenzyl amine; isoquinoline; 4-benzyl pyridine,N,N-dimethyldodecyl amine, triethyl amine, and the like. A variety ofother catalysts for imidization are known in the art, such asimidazoles, and may be useful in accordance with the present disclosure.

The conversion chemicals can generally react at about room temperatureor above to convert polyamic acid to polyimide. In one embodiment, thechemical conversion reaction occurs at temperatures from 15° C. to 120°C. with the reaction being very rapid at the higher temperatures andrelatively slower at the lower temperatures.

In one embodiment, the chemically treated polyamic acid solution can becast or extruded onto a heated conversion surface or substrate. In oneembodiment, the chemically treated polyamic acid solution can be cast onto a belt or drum. The solvent can be evaporated from the solution, andthe polyamic acid can be partially chemically converted to polyimide.The resulting solution then takes the form of a polyamic acid-polyimidegel. Alternately, the polyamic acid solution can be extruded into a bathof conversion chemicals consisting of an anhydride component(dehydrating agent), a tertiary amine component (catalyst) or both withor without a diluting solvent. In either case, a gel film is formed andthe percent conversion of amic acid groups to imide groups in the gelfilm depends on contact time and temperature but is usually about 10 to75 percent complete. For curing to a solids level greater than 98%, thegel film typically must be dried at elevated temperature (from about200° C., up to about 550° C.), which will tend to drive the imidizationto completion. In some embodiments, the use of both a dehydrating agentand a catalyst is preferred for facilitating the formation of a gel filmand achieve desired conversion rates.

The gel film tends to be self-supporting in spite of its high solventcontent. Typically, the gel film is subsequently dried to remove thewater, residual solvent, and remaining conversion chemicals, and in theprocess the polyamic acid is essentially completely converted topolyimide (i.e., greater than 98% imidized). The drying can be conductedat relatively mild conditions without complete conversion of polyamicacid to polyimide at that time, or the drying and conversion can beconducted at the same time using higher temperatures.

Because the gel has so much liquid that must be removed during thedrying and converting steps, the gel generally must be restrained duringdrying to avoid undesired shrinkage. In continuous production, the basefilm can be held at the edges, such as in a tenter frame, using tenterclips or pins for restraint.

High temperatures can be used for short times to dry the base film andinduce further imidization to convert the gel film to a polyimide basefilm in the same step. In one embodiment, the base film is heated to atemperature of 200° C. to 550° C. Generally, less heat and time arerequired for thin films than for thicker films.

During such drying and converting (from polyamic acid to polyimide), thebase film can be restrained from undue shrinking and, in fact, may bestretched by as much as 150 percent of its initial dimension. In filmmanufacture, stretching can be in either the longitudinal direction orthe transverse direction or both. If desired, restraint can also beadjusted to permit some limited degree of shrinkage.

Another advantage is the chemically converted base films of the presentdisclosure are matte on both sides, even if cast onto a smooth surface.If both sides of the base film are matte, any additional layers may beapplied to either side of the base film. In contradistinction, whensimilarly filled polyimide precursor films are solely thermallyconverted and cast on a smooth surface, the cast side tends to be glossyand the air side tends to be matte.

Yet another advantage is chemically converted base films have higherdielectric strength compared to solely thermally converted base film.Typically, the dielectric strength decreases as the amount of mattingagent increases. So while low 60 degree gloss value can be achieved (airside only) in the solely thermal process, by increasing the amount ofmatting agent, the dielectric strength will decrease.

In one embodiment, the polyamic acids are made by dissolvingapproximately equimolar amounts of a dianhydride and a diamine in asolvent and agitating the resulting solution under controlledtemperature conditions until polymerization of the dianhydride and thediamine is completed. Typically a slight excess of one of the monomers(usually diamine) is used to initially control the molecular weight andviscosity which can then be increased later via small additional amountsof the deficient monomer. Examples of suitable dianhydrides for use inthe polyimides of the present disclosure include aromatic dianhydrides,aliphatic dianhydrides and mixtures thereof. In one embodiment, thearomatic dianhydride is selected from the group consisting of:

-   pyromellitic dianhydride;-   3,3′,4,4′-biphenyl tetracarboxylic dianhydride;-   3,3′,4,4′-benzophenone tetracarboxylic dianhydride;-   4,4′-oxydiphthalic anhydride;-   3,3′,4,4′-diphenyl sulfone tetracarboxylic dianhydride;-   2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane;-   Bisphenol A dianhydride; and-   mixtures and derivatives thereof.    In another embodiment, the aromatic dianhydride is selected from the    group consisting of:-   2,3,6,7-naphthalene tetracarboxylic dianhydride;-   1,2,5,6-naphthalene tetracarboxylic dianhydride;-   2,2′,3,3′-biphenyl tetracarboxylic dianhydride;-   2,2-bis(3,4-dicarboxyphenyl)propane dianhydride;-   bis(3,4-dicarboxyphenyl)sulfone dianhydride;-   3,4,9,10-perylene tetracarboxylic dianhydride;-   1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride;-   1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride;-   bis(2,3-dicarboxyphenyl)methane dianhydride;-   bis(3,4-dicarboxyphenyl)methane dianhydride;-   oxydiphthalic dianhydride;-   bis(3,4-dicarboxyphenyl)sulfone dianhydride;-   mixtures and derivatives thereof.    Examples of aliphatic dianhydrides include-   cyclobutane dianhydride;-   [1S*,5R*,6S]-3-oxabicyclo[3.2.1]octane-2,4-dione-6-spiro-3-(tetrahydrofuran-2,5-dione);-   mixtures thereof.

Examples of suitable diamines for use in the polyimides of the presentdisclosure include aromatic diamines, aliphatic diamines and mixturesthereof. In one embodiment, the aromatic diamine is selected from agroup consisting of:

-   3,4′-oxydianiline;-   1,3-bis-(4-aminophenoxy)benzene;-   4,4′-oxydianiline;-   1,4-diaminobenzene;-   1,3-diaminobenzene;-   2,2′-bis(trifluoromethyl)benzidene;-   4,4′-diaminobiphenyl;-   4,4′-diaminodiphenyl sulfide;-   9,9′-bis(4-amino)fluorine;-   mixtures and derivatives thereof.    In another embodiment, the aromatic diamine is selected from a group    consisting of:-   4,4′-diaminodiphenyl propane;-   4,4′-diamino diphenyl methane;-   benzidine;-   3,3′-dichlorobenzidine;-   3,3′-diamino diphenyl sulfone;-   4,4′-diamino diphenyl sulfone;-   1,5-diamino naphthalene;-   4,4′-diamino diphenyl diethylsilane;-   4,4′-diamino diphenysilane;-   4,4′-diamino diphenyl ethyl phosphine oxide;-   4,4′-diamino diphenyl N-methyl amine;-   4,4′-diamino diphenyl N-phenyl amine;-   1,4-diaminobenzene(p-phenylene diamine);-   1,2-diaminobenzene;-   Mixtures and derivatives thereof.    Examples of suitable aliphatic diamines include-   hexamethylene diamine,-   dodecane diamine,-   cyclohexane diamine;-   and mixtures thereof.

In one embodiment, the chemically converted polyimide is derived frompyromellitic dianhydride (“PMDA”) and 4,4′-oxydianiline (“4,4 ODA”). Inone embodiment, the polyimides of the present disclosure arecopolyimides derived from any of the above diamines and dianhydrides. Inone embodiment, the copolyimide is derived from 15 to 85 mole % ofbiphenyltetracarboxylic dianhydride, 15 to 85 mole % pyromelliticdianhydride, 30 to 100 mole % p-phenylenediamine and optionallyincluding 0 to 70 mole % of 4,4′-diaminodiphenyl ether and/or4,4′-diaminodiphenyl ether. Such copolyimides are further described inU.S. Pat. No. 4,778,872 and U.S. Pat. No. 5,166,308.

In one embodiment, the polyimide dianhydride component is pyromelliticdianhydride (“PMDA”) and the polyimide diamine component is acombination of 4,4′-oxydianiline (“4,4 ODA”) and p-phenylenediamine(“PPD”). In one embodiment the polyimide dianhydride component ispyromellitic dianhydride (“PMDA”) and the polyimide diamine component isa combination of 4,4′-oxydianiline (“4,4 ODA”) and p-phenylenediamine(“PPD”), where the ratio of ODA to PPD (ODA:PPD) is any of the followingmole ratios: i. 20-80:80-20; ii. 50-70:50-30; or iii. 55-65:45-35. Inone embodiment the polyimide dianhydride component is PMDA, and thediamine component is a mole ratio of ODA to PPD (ODA:PPD) of about60:40.

In one embodiment, the polyimide dianhydride component is3,3′,4,4′-biphenyltetracarboxylic dianhydride (“BPDA”) and the polyimidediamine component is a combination of 4,4′-oxydianiline (“4,4 ODA”) andp-phenylenediamine (“PPD”). In one embodiment the polyimide dianhydridecomponent is BPDA and the polyimide diamine component is a combinationof 4,4 ODA and PPD, where the ratio of ODA to PPD (ODA:PPD) is any ofthe following mole ratios: i. 20-80:80-20; ii. 50-70:50-30; or iii.55-65:45-35. In one embodiment the polyimide dianhydride component isBPDA, and the diamine component is a mole ratio of ODA to PPD (ODA:PPD)of about 60:40.

In one embodiment, the polyamic acid solvent must dissolve one or bothof the polymerizing reactants and in one embodiment, will dissolve thepolyamic acid polymerization product. The solvent should besubstantially unreactive with all of the polymerizing reactants and withthe polyamic acid polymerization product.

In one embodiment the polyamic acid solvent is a liquidN,N-dialkylcarboxylamide, such as, a lower molecular weightcarboxylamide, particularly N,N-dimethylformamide andN,N-diethylacetamide. Other useful compounds of this class of solventsare N,N-diethylformamide and N,N-diethylacetamide. Other solvents whichmay be used are sulfolane, N-methyl-2-pyrrolidone, tetramethyl urea,dimethylsulfone, and the like. The solvents can be used alone or incombinations with one another. The amount of solvent used preferablyranges from 75 to 90 weight % of the polyamic acid.

The polyamic acid solutions are generally made by dissolving the diaminein a dry solvent and slowly adding the dianhydride under conditions ofagitation and controlled temperature in an inert atmosphere.

Pigment

Virtually any pigment (or combination of pigments) can be used in theperformance of the present invention. In some embodiments, usefulpigments include but are not limited to the following: Barium LemonYellow, Cadmium Yellow Lemon, Cadmium Yellow Lemon, Cadmium YellowLight, Cadmium Yellow Middle, Cadmium Yellow Orange, Scarlet Lake,Cadmium Red, Cadmium Vermilion, Alizarin Crimson, Permanent Magenta, VanDyke brown, Raw Umber Greenish, or Burnt Umber. In some embodiments,useful black pigments include: cobalt oxide, Fe—Mn—Bi black, Fe—Mn oxidespinel black, (Fe,Mn)2O3 black, copper chromite black spinel, lampblack,bone black, bone ash, bone char, hematite, black iron oxide, micaceousiron oxide, black complex inorganic color pigments (CICP), CuCr2O4black, (Ni,Mn,Co)(Cr,Fe)2O4 black, Aniline black, Perylene black,Anthraquinone black, Chromium Green-Black Hematite, Chrome Iron Oxide,Pigment Green 17, Pigment Black 26, Pigment Black 27, Pigment Black 28,Pigment Brown 29, Pigment Black 30, Pigment Black 32, Pigment Black 33or mixtures thereof.

In some embodiments, a low conductivity carbon black is used. The amountof low conductivity carbon black and the thickness of the base film willgenerally impact the optical density. If the low conductivity carbonblack loading level is unduly high, the base film will be conductiveeven when a low conductivity carbon black is used. If too low, the basefilm may not achieve the desired optical density and color. The lowconductivity carbon black, for the purpose of this disclosure, is usedto impart the black color to the base film as well as to achieve thedesired optical density of a base film having a thickness between andoptionally including any two of the following: 8, 10, 15, 20, 25, 30,35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140 and 152 microns.In some embodiments, the base film thickness is from 8 to 152 microns.In some embodiments, the base film thickness is from 8 to 127 microns.In yet another embodiment, the base film thickness is from 10 to 40microns. Low conductivity carbon black is intended to mean, channel typeblack or furnace black. In some embodiments a bone black may be used toimpart the black color. In one embodiment, the low conductivity carbonblack is present in amount between and optionally including any two ofthe following: 2, 3, 4, 5, 6, 7, 8 and 9 weight percent of the basefilm. In some embodiments, the optical density (opacity) desirable(e.g., to hide the conductor traces in the flex circuits from view) isgreater than or equal to 2. An optical density of 2 is intended to mean1×10⁻² or 1% of light is transmitted through the base film.

In some embodiments, the low conductivity carbon black is a surfaceoxidized carbon black. One method for assessing the extent of surfaceoxidation (of the carbon black) is to measure the carbon black'svolatile content. The volatile content can be measured by calculatingweight loss when calcined at 950° C. for 7 minutes. Generally speaking,a highly surface oxidized carbon black (high volatile content) can bereadily dispersed into a polyamic acid solution (polyimide precursor),which in turn can be imidized into a (well dispersed) filled polyimidebase polymer of the present disclosure. It is thought that if the carbonblack particles (aggregates) are not in contact with each other, thenelectron tunneling, electron hopping or other electron flow mechanismare generally suppressed, resulting in lower electrical conductivity. Insome embodiments, the low conductivity carbon black has a volatilecontent greater than or equal to 1%. In some embodiments, the lowconductivity carbon black has a volatile content greater than or equalto 5, 9, or 13%. In some embodiments, furnace black may be surfacetreated to increase the volatile content.

A uniform dispersion of isolated, individual particles (aggregates) notonly decreases the electrical conductivity, but additionally tends toproduce uniform color intensity. In some embodiments the lowconductivity carbon black is milled. In some embodiments, the meanparticle size of the low conductivity carbon black is between (andoptionally including) any two of the following sizes: 0.2, 0.3, 0.4,0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 microns. The thickness of the base filmcan be tailored to the specific application.

In some embodiments, dyes may be used. Examples of useful dye are, butnot limited to nigrosin black, monoazo chromium complex black, ormixtures thereof. In some embodiments, a mixture of dye and pigment maybe used.

Matting Agent

Polymeric materials typically have inherent surface gloss. To controlgloss (and thereby produce matte surface characteristics) variousadditive approaches are possible to achieve dull and low gloss surfacecharacteristics. Broadly speaking, the additive approaches are all basedupon the same fundamental physics—to create a modified surface which is(on a micro-scale) coarse and irregular shaped and therefore allows lesslight to be reflected back to the distant (e.g., greater than 50centimeters) observer. When multiple rays of light hit a glossy surface,most of the light is reflected with similar angle and therefore arelatively high level of light reflectance can be observed. When thesame source of light hits a matte (ie. irregular) surface, the light isscattered in many different directions and also a much higher fractionis absorbed. Hence on rough surfaces, light tends to be diffuselyscattered in all directions, and the image forming qualities are largelydiminished (reflected objects no longer appear brilliant, but blurred).

Gloss meters used to characterize a specific surface for gloss level arebased on this same principle. Typically, a light source hits a surfaceat a fixed angle and after reflection the amount of reflected light isread by a photo cell. Reflection can be read at multiple angles. Maximumgloss performance for a perfectly glossy surface tends to demonstrate100% reflection, whereas a fully dull surface tends to demonstrate 0%reflection.

Silicas are inorganic particles that can be ground and filtered tospecific particle size ranges. The very irregular shape and porosity ofsilica particles and low cost make it a popular matting agent. Otherpotential matting agents can include: i, other ceramics, such as,borides, nitrides, carbides and other oxides (e.g., alumina, titania,etc); and ii, organic particles, provided the organic particle canwithstand the temperature processing of a chemically converted polyimide(processing temperatures of from about 250° C. to about 550° C.,depending upon the particular polyimide process chosen). One mattingagent that can be useful in polyimide applications (can withstand thethermal conditions of polyimide synthesis) is polyimide particles.

The amount of matting agent, median particle size and density must besufficient to produce the desired 60 degree gloss value. In someembodiments, the base film 60 degree gloss value is between andoptionally including any two of the following: 2, 5, 10, 15, 20, 25, 30and 35. In some embodiments, the base film 60 degree gloss value is from10 to 35.

In some embodiments, the matting agent is present in an amount betweenand optionally including any two of the following: 1.6, 2, 3, 4, 5, 6,7, 8, 9 and 10 weight percent of base film. In some embodiments, thematting agent has a median particle size between and optionallyincluding any two of the following: 1.3, 2, 3, 4, 5, 6, 7, 8, 9 and 10microns. The matting agent particles should have an average particlesize of less than (or equal to) about 10 microns and greater than (orequal to) about 1.3 microns. Larger matting agent particles maynegatively impact mechanical properties of the final base film. In someembodiments, the matting agent has a density between and optionallyincluding any two of the following: 2, 3, 4 and 4.5 g/cc. In someembodiments, when the amount of matting agent is below 1.6 weightpercent of base film, the desired 60 degree gloss value is not achievedeven when the matting agent median particle size and density are in thedesired ranges. In some embodiments, when the median particle size isbelow 1.3 microns, the desired 60 degree gloss value is not achievedeven when the amount of matting agent and density are in the desiredranges. In some embodiments, the matting agent is selected from thegroup consisting of silica, alumina, barium sulfate and mixturesthereof.

The base film can be prepared by any method well known in the art formaking a chemically converted, filled polyimide layer. In one suchembodiment, a slurry comprising a low conductivity carbon black isprepared and a matting agent slurry is prepared. The slurries may or maynot be milled using a ball mill to reach the desired particle size. Theslurries may or may not be filtered to remove any residual largeparticles. A polyamic acid solution can be made by methods well known inthe art. The polyamic acid solution may or may not be filtered. In someembodiments, the solution is mixed in a high shear mixer with the lowconductivity carbon black slurry and the matting agent slurry. When apolyamic acid solution is made with a slight excess of diamine,additional dianhydride solution may or may not be added to increase theviscosity of the mixture to the desired level for film casting. Theamount of the polyamic acid solution, low conductivity carbon blackslurry, and matting agent slurry can be adjusted to achieve the desiredloading levels in the cured base film. In some embodiments the mixtureis cooled below 0° C. and mixed with conversion chemicals prior tocasting onto a heated rotating drum or belt in order to produce apartially imidized gel film. The gel film may be stripped from the drumor belt, placed on a tenter frame, and cured in an oven, usingconvective and radiant heat to remove solvent and complete theimizidation to greater than 98% solids level.

Adhesive

In some embodiments, the base film is a multilayer film comprising thebase film and an adhesive layer. The base film of the present disclosurecan comprise an adhesive layer for maintaining the base film in place,once applied. In one embodiment, the adhesive consists of an epoxy resinand hardener, and, optionally, further contains additional components,such as, an elastomer, curing accelerator (catalyst), hardener, fillerand flame retardant.

In some embodiments, the adhesive is an epoxy resin. In someembodiments, the epoxy resin is selected from the group consisting of:

Bisphenol F type epoxy resin,

Bisphenol S type epoxy resin,

Phenol novolac type epoxy resin,

Biphenyl type epoxy resin,

Biphenyl aralkyl type epoxy resin,

Aralkyl type epoxy resin,

Dicyclopetadiene type epoxy resin,

Multifunctional type epoxy resin,

Naphthalene type epoxy resin,

Rubber modified epoxy resin, and

mixtures thereof.

In another embodiment, the adhesive is an epoxy resin selected from thegroup consisting of bisphenol A type epoxy resin, cresol novolac typeepoxy resin, phosphorus containing epoxy resin, and mixtures thereof. Insome embodiments, the adhesive is a mixture of two or more epoxy resins.In some embodiments, the adhesive is a mixture of the same epoxy resinhaving different molecular weights.

In some embodiments, the epoxy adhesive contains a hardener. In oneembodiment, the hardener is a phenolic compound. In some embodiments,the phenolic compound is selected from the group consisting of:

Novolac type phenol resin,

Aralkyl type phenol resin,

Biphenyl aralkyl type phenol resin,

Multifunctional type phenol resin,

Nitrogen containing phenol resin,

Dicyclopetadiene type phenol resin,

Phosphorus containing phenol resin, and

Triazine containing phenol novolac resin.

In another embodiment, the hardener is an aromatic diamine compound. Insome embodiments, the aromatic diamine compound is a diaminobiphenylcompound. In some embodiments, the diaminobiphenyl compound is4,4′-diaminobiphenyl or 4,4′-diamino-2,2′-dimethylbiphenyl. In someembodiments, the aromatic diamine compound is a diaminodiphenylalkanecompound. In some embodiments, the diaminodiphenylalkane compound is4,4′-diaminodiphenylmethane or 4,4′-diaminodiphenylethane. In someembodiments, the aromatic diamine compound is a diaminodiphenyl ethercompound. In some embodiments, the diaminodiphenyl ether compounds is4,4′-diaminodiphenylether or di(4-amino-3-ethylphenyl)ether. In someembodiments, the aromatic diamine compound is a diaminodiphenylthioether compound. In some embodiments, the diaminodiphenyl thioethercompound is 4,4′-diaminodiphenyl thioether ordi(4-amino-3-propylphenyl)thioether. In some embodiments, the aromaticdiamine compound is a diaminodiphenyl sulfone compound. In someembodiments, the diaminodiphenyl sulfone compound is4,4′-diaminodiphenyl sulfone or di(4-amino-3-isopropylphenyl)sulfone. Insome embodiments, the aromatic diamine compound is phenylenediamine. Inone embodiment, the hardener is an amine compound. In some embodiments,the amine compound is a guanidine. In some embodiments, the guanidine isdicyandiamide (DICY). In another embodiment, the amine compound is analiphatic diamine. In some embodiments, the aliphatic diamine isethylenediamine or diethylenediamine.

In some embodiments, the epoxy adhesive contains a catalyst. In someembodiments, the catalyst is selected from the group consisting ofimidazole type, triazine type, 2-ethyl-4-methyl-imidazole, triazinecontaining phenol novolac type and mixtures thereof.

In some embodiments, the epoxy adhesive contains a elastomer tougheningagent. In some embodiments, the elastic toughening agent is selectedfrom the croup consisting of ethylene-acryl rubber,acrylonitrile-butadiene rubber, carboxy terminatedacrylonitrile-butadiene rubber and mixtures thereof.

In some embodiments, the epoxy adhesive contains a flame retardant. Insome embodiments, the flame retardant is selected from the groupconsisting of aluminum trihydroxide, melamine polyphosphate, condensedpolyphosphate ester, other phosphorus containing flame retardants andmixtures thereof.

In some embodiments, the adhesive layer is selected from the groupconsisting of:

polyimide,

butyral phenolic,

polysiloxane,

polyimidesiloxane,

fluorinated ethylene propylene copolymers,

perfluoroalkoxy copolymers,

ethylene vinyl acetate copolymers,

ethylene vinyl acetate glycidyl acrylate terpolymer,

ethylene vinyl acetate glycidyl methacrylate terpolymer,

ethylene alkyl acrylate copolymers with adhesion promotor,

ethylene alkyl methacrylate copolymers with adhesion promotor,

ethylene glycidyl acrylate,

ethylene glycidyl methacrylate,

ethylene alkyl acrylate glycidyl acrylate terpolymer,

ethylene alkyl methacrylate glycidyl acrylate terpolymer,

ethylene alkyl acrylate maleic anhydride terpolymers,

ethylene alkyl methacrylate maleic anhydride terpolymers,

ethylene alkyl acrylate glycidyl methacrylate terpolymers,

ethylene alkyl methacrylate glycidyl methacrylate terpolymers,

alkyl acrylate acrylonitrile acrylic acid terpolymers,

alkyl acrylate acrylonitrile methacrylic acid terpolymers,

ethylene acrylic acid copolymer including salts thereof,

ethylene methacrylic acid copolymer including salts thereof,

alkyl acrylate acrylonitrile glycidyl methacrylate terpolymers,

alkyl methacrylate acrylonitrile glycidyl methacrylate terpolymers,

alkyl acrylate acrylonitrile glycidyl acrylate terpolymers,

alkyl methacrylate acrylonitrile glycidyl acrylate terpolymers,

polyvinyl butyral,

ethylene alkyl acrylate methacrylic acid terpolymers and salts thereof,

ethylene alkyl methacrylate methacrylic acid terpolymers and saltsthereof,

ethylene alkyl acrylate acrylic acid terpolymers and salts thereof

ethylene alkyl methacrylate acrylic acid terpolymers and salts thereof,

ethylene ethyl hydrogen maleate,

ethylene alkyl acrylate ethyl hydrogen maleate,

ethylene alkyl methacrylate ethyl hydrogen maleate,

and mixtures thereof.

In some embodiments, the multilayer film is a coverlay film.

In the following examples all parts and percentages are by weight unlessotherwise indicated.

EXAMPLES

The invention will be further described in the following examples, whichis not intended to limit the scope of the invention described in theclaims.

Optical density was measured with a Macbeth TD904 optical densitometer.The average of 5-10 individual measurements was recorded.

60 degree gloss value was measured with a Micro-TRI-Gloss gloss meter,Gardner USA, Columbia, Md. The average of 5-10 individual measurementswas recorded.

Surface resistivity was measured using a Advantest Model R8340 ultrahigh resistance meter with a UR type concentric ring probe and wasmeasured at 1000 volts. The average of 3-5 individual measurements wasrecorded.

Dielectric strength was measured using a Beckman Industrial ACDielectric Breakdown Tester, according to ASTM D149. The average of 5-10individual measurements was recorded.

Median particle size was measured using a Horiba LA-930 particle sizeanalyzer. Horiba, Instruments, Inc., Irvine Calif. DMAC(dimethylacetamide) was used as the carrier fluid.

When a continuous film casting process was used to produce samples, anashing process was used to confirm the amount of matting agent in thefilm. The film was ashed by heating in a furnace at 900° C. to burn offall of the polymer and low conductivity carbon black, leaving only awhite matting agent residue. Comparing weights before and after ashingshows the amount of matting agent the film contains.

Polyamic acid viscosity measurements were made on a BrookfieldProgrammable DV-II+ viscometer using either an RV/HA/HB #7 spindle or anLV #5 spindle. The viscometer speed was varied from 5 to 100 rpm toprovide an acceptable percent torque value. Readings were temperaturecorrected to 25° C.

Examples 1-5 demonstrate that chemical conversion achieves low 60 degreegloss value (matte appearance) on both sides of base film as well ashigh dielectric strength with low amounts of matting agent.

Example 1

A carbon black slurry was prepared, consisting of 80 wt % DMAC, 10 wt %polyamic acid prepolymer solution (20.6 wt % polyamic acid solids inDMAC), and 10 wt % low conductivity carbon black powder (Special Black4, from Evonik Degussa). The ingredients were thoroughly mixed in arotor stator, high-speed dispersion mill. The slurry was then processedin a ball mill to disperse any large agglomerates and to achieve thedesired particle size. The median particle size of the slurry was 0.3microns.

A silica slurry was prepared, consisting of 75.4 wt % DMAC, 9.6 wt %polyamic acid prepolymer solution (20.6 wt % polyamic acid solids inDMAC), and 15.0 wt % silica powder (Syloid® C 803, from W. R. GraceCo.). The ingredients were thoroughly mixed in a high shear rotor-statortype mixer. Median particle size was 3.3-3.6 microns.

16.4 kg of the carbon black slurry was mixed into 158 kg of aPMDA/4,4′ODA prepolymer solution (20.6% polyamic acid solids,approximately 50 Poise viscosity) in a 50 gallon (189.3 liters) tank.The tank was equipped with three independently controlled agitatorshafts: a low speed anchor mixer, a high speed disk disperser, and ahigh shear rotor-stator emulsifier. The mixture was “finished” by addingand mixing, in increments, approximately 7 kg. of a 5.8 wt % PMDAsolution in DMAC, in order to increase molecular weight and viscosity toapproximately 3000 Poise. The speeds of the anchor, disperser, andemulsifier were adjusted as necessary to ensure efficient mixing anddispersion, without excessively heating the mixture. Temperature of themixture was further regulated by flowing chilled ethylene glycol throughthe mixing tank jacket. The finished solution was filtered through a 20micron filter and vacuum degassed to remove entrained air.

The silica slurry was metered into a metered stream of the finishedpolymer/carbon black mixture and thoroughly mixed using a high shearrotor-stator mixer. The combined stream was cooled to approximately 6°C., conversion chemicals acetic anhydride (0.14 cm³/cm³ polymersolution) and 3-picoline (0.15 cm³/cm³ polymer solution) were metered inand mixed, and a film was cast using a slot die, onto a 90° C. hot,rotating drum. The resulting gel film was stripped off the drum and fedinto a tenter oven, where it was dried and cured to a solids levelgreater than 98%, using convective and radiant heating. The base filmcontained 5 wt % carbon black and 3.5 wt % silica.

Results are shown in table 1.

Example 2

An alumina slurry was prepared, consisting of 41.7 wt % DMAC, 23.3 wt %polyamic acid prepolymer solution (20.6 wt % polyamic acid solids inDMAC), and 35.0 wt % alpha alumina powder with median particle size ofapproximately 2.2 microns. The ingredients were thoroughly mixed in arotor stator, high-speed dispersion mill.

The alumina slurry was metered into a cooled (−7° C.) metered stream ofthe finished polymer/carbon black mixture of Example 1, along with theconversion chemicals, and a polyimide film was cast and cured usingessentially the same process as Example 1. The resulting base filmcontains 5 wt % carbon black and 7 wt % alumina.

Results are shown in table 1.

Example 3

Carbon black and silica slurries were prepared as in Example 1. Theslurries were mixed with PMDA/4,4′ODA prepolymer solution (20.6%polyamic acid solids, approximately 50 Poise viscosity), in amounts toyield 5 wt % carbon black and 2 wt % silica on a cured film basis. Themixture was finished by incrementally adding a 6 wt % solution of PMDAin DMAC, with mixing, to achieve a final viscosity of approximately 2250Poise. The finished polymer mixture was vacuum degassed. Using astainless steel casting rod, the polymer mixture was manually cast ontoa Mylar® polyethylene terephthalate sheet attached to a glass plate. TheMylar® polyethylene terephthalate sheet containing the wet cast film wasimmersed in a bath consisting of a 50/50 mixture of 3-picoline andacetic anhydride. The bath was gently agitated for a period of 3 to 4minutes in order to effect imidization and gellation of the film. Thegel film was peeled from the Mylar® polyethylene terephthalate sheet andplaced on a pin frame to restrain the film and prevent shrinking. Afterallowing for residual solvent to drain from the film, the pin framecontaining the film was placed in a 120° C. oven. The oven temperaturewas ramped to 320° C. over a period of 60 to 75 minutes, held at 320° C.for 10 minutes, then transferred to a 400° C. oven and held for 5minutes, then removed from the oven and allowed to cool.

Results are shown in table 1.

Example 4

The base film was prepared as in Example 3 with 3 wt % silica on a curedfilm basis.

Results are shown in table 1.

Example 5

A carbon black slurry was prepared as in Example 1. A synthetic bariumsulfate (Blanc Fixe F, from Sachtleben Chemie GmbH) slurry was prepared,consisting of 51.7 wt % DMAC, 24.1 wt % prepolymer solution (20.6 wt %polyamic acid solids in DMAC) and 24.1 wt % barium sulfate powder. Theingredients were thoroughly mixed in a high shear rotor-stator typemixer. Median particle size was 1.3 microns.

The slurries were mixed with PMDA/4,4′ODA polyamic acid solution (20.6%polyamic acid solids, approximately 50 Poise viscosity), in amounts toyield 7 wt % carbon black and 10 wt % barium sulfate on a cured filmbasis. The mixture was finished by incrementally adding a 6 wt %solution of PMDA in DMAC, with mixing, to achieve a final viscosity of2400 Poise. The finished polymer mixture was vacuum degassed. Thepolymer mixture was cast onto Mylar® polyethylene terephthalate sheetand chemically imidized and cured as described in Example 3.

Results are shown in table 1.

Comparative Example 1

Comparative example 1 demonstrates thermal conversion with the sameamount of matting agent as in example 5, produces a high (undesirable)60 degree gloss value on both sides of base film and low dielectricstrength.

A carbon black slurry was prepared as in Example 1. A synthetic bariumsulfate (Blanc Fixe F, from Sachtleben Chemie GmbH) slurry was prepared,consisting of 51.7 wt % DMAC, 24.1 wt % polyamic acid prepolymersolution (20.6 wt % polyamic acid solids in DMAC), and 24.1 wt % bariumsulfate powder. The ingredients were thoroughly mixed in a high shearrotor-stator type mixer. Median particle size was 1.3 microns.

The slurries were mixed with PMDA/4,4′ODA prepolymer solution (20.6%polyamic acid solids, approximately 50 Poise viscosity), in amounts toyield 7 wt % carbon black and 10 wt % barium sulfate on a cured filmbasis. The mixture was finished by incrementally adding a 6 wt %solution of PMDA in DMAC, with mixing, to achieve a final viscosity of1500 Poise. The finished polymer mixture was vacuum degassed. Using astainless steel casting rod, a film was manually cast onto a glassplate. The glass plate containing the wet cast film was placed on a hotplate at 80-100° C. for 30-45 minutes to form a partially dried,partially imidized “green” film. The green film was peeled from theglass and placed on a pin frame. The pin frame containing the green filmwas placed in a 120° C. oven. The oven temperature was ramped to 320° C.over a period of 60-75 minutes, held at 320° C. for 10 minutes, thentransferred to a 400° C. oven and held for 5 minutes, then removed fromthe oven and allowed to cool.

Results are shown in table 1.

Comparative Example 2

Comparative example 2 demonstrates thermal conversion with 4 weight %matting agent produces a high (undesirable) 60 degree gloss value onboth sides of base film and has low dielectric strength.

Carbon black and silica slurries were prepared as in Example 1.

The slurries were mixed with PMDA/4,4′ODA prepolymer solution (20.6%polyamic acid solids, approximately 50 Poise viscosity), in amounts toyield 5 wt % carbon black and 4 wt % silica on a cured film basis. Themixture was finished by incrementally adding a 6 wt % solution of PMDAin DMAC, with mixing, to achieve a final viscosity of 2250 Poise. Thefinished polymer mixture was vacuum degassed. Using a stainless steelcasting rod, a film was manually cast onto a glass plate. The glassplate containing the wet cast film was placed on a hot plate at 80-100°C. for 30-45 minutes to form a partially dried, partially imidized“green” film. The green film was peeled from the glass and placed on apin frame. The pin frame containing the green film was placed in a 120°C. oven. The oven temperature was ramped to 320° C. over a period of60-75 minutes, held at 320° C. for 10 minutes, then transferred to a400° C. oven and held for 5 minutes, then removed from the oven andallowed to cool.

Results are shown in table 1.

Comparative Example 3

Comparative Example 3 demonstrates thermal conversion requires a higheramount of matting agent to produce a low 60 degree gloss value (matteappearance) on the air side yet has an undesirable 60 degree gloss valueon the other (non air) side.

A carbon black slurry was prepared as in Example 1. An alumina slurrywas prepared, consisting of 51.72 wt % DMAC, 24.14 wt % polyamic acidprepolymer solution (20.6 wt % polyamic acid solids in DMAC), and 24.14wt % alpha alumina powder with median particle size of 2.3 microns. Theingredients were thoroughly mixed in a rotor stator, high-speeddispersion mill. The slurry was then milled in a ball mill to break downlarge agglomerates. The carbon black and alumina slurries were filteredto remove any residual large particles or agglomerates.

A PMDA/4,4′ODA prepolymer solution (20.6% polyamic acid solids,approximately 50 Poise viscosity) was “finished” by mixing in a highshear mixer with a 5.8 wt % PMDA solution in DMAC, in order to increasemolecular weight and the viscosity to approximately 1500 Poise. Thefinished solution was filtered and mixed in a high shear mixer with thelow conductivity carbon black and alumina slurries, along withadditional PMDA finishing solution, and a small amount of a belt releaseagent (which enables the cast green film to be readily stripped from thecasting belt). The quantity of PMDA finishing solution was adjusted toachieve a viscosity of 1200 Poise. The relative amounts of the polymer,slurries, and finishing solution were adjusted in order to achieve thedesired loading levels of carbon black and alumina, and pressure at thecasting die. The finished polymer/slurry mixture was pumped through afilter and to a slot die, where the flow was divided in such a manner asto form the outer layers of a three-layer coextruded film.

A second stream of PMDA/4,4′ODA prepolymer polymer solution, wasfinished in a high shear mixer to 1500 Poise viscosity and was pumpedthrough a filter and to the casting die to form the middle, unfilledpolyimide core layer of a three-layer coextruded film. The flow rates ofthe outer layers as well as the unfilled polyimide core layer solutionswere adjusted in order to achieve the desired layer thickness.

A three-layer coextruded film was produced from the components describedabove by casting from the slot die onto a moving stainless steel belt.The belt was passed into a convective oven, to evaporate solvent andpartially imidize the polymer, to produce a “green” film. Green filmsolids (as measured by weight loss upon heating to 300° C.) were 72.6%.The green film was stripped off the casting belt and wound up. The greenfilm was then passed through a tenter oven to produce a cured polyimidefilm. During tentering, shrinkage was controlled by constraining thefilm along the edges. Cured film solids level (as measured by weightloss upon heating to 300° C.) was 98.8%.

The middle unfilled layer comprised 33% or ⅓ of the total thickness ofthe multilayer film and the outer layers contained alumina and lowconductivity carbon black of equal thickness. The outer layers contained7 wt low conductivity carbon black and 30 wt % alumina. Total filmthickness was 0.49 mils.

Results are shown in table 1.

Comparative Examples 4 and 5 demonstrate some amount of matting agent isneeded to achieve low 60 degree gloss value (matte appearance) on bothsides of base film and further demonstrate that a matting agent withparticle size below 1.3 microns gives a glossy base film.

Comparative Example 4

A carbon black slurry having a median particle size of 0.3 microns wasprepared as in Example 1. The slurry was mixed with PMDA/4,4′ODAprepolymer solution (20.6% polyamic acid solids, approximately 50 Poiseviscosity), in an amount to yield 7 wt % carbon black on a cured filmbasis. The mixture was finished by incrementally adding a 6 wt %solution of PMDA in DMAC, with mixing, to achieve a final viscosity of1900 Poise. The finished polymer mixture was vacuum degassed. Thepolymer mixture was cast onto Mylar® polyethylene terephthalate sheetand chemically imidized and cured as described in Example 3.

Results are shown in table 1.

Comparative Example 5

To a metered stream of the finished polyamic acid/carbon black mixtureof Example 1, additional carbon black slurry was metered, so as toincrease the carbon black content to 7 wt % on a cured film basis, andthe two steams were thoroughly mixed using a high shear rotor-statormixer. A chemically imidized base film was produced as described inExample 1.

Results are shown in table 1.

Comparative Example 6

Comparative example 6 demonstrates chemical conversion with 30 wt % ofBaSO₄ does show the expected decrease in dielectric strength comparedwith example 5 chemical conversion having 10 wt % BaSO₄. Butsurprisingly chemical conversion with 30 wt % of BaSO₄ has higherdielectric strength compared to comparative example 1 thermal conversionhaving 10 wt % BaSO₄.

A carbon black slurry was prepared as in Example 1. A synthetic bariumsulfate (Blanc Fixe F, from Sachtleben Chemie GmbH) slurry was prepared,consisting of 51.7 wt % DMAC, 24.1 wt % prepolymer solution (20.6 wt %polyamic acid solids in DMAC) and 24.1 wt % barium sulfate powder. Theingredients were thoroughly mixed in a high shear rotor-stator typemixer. Median particle size was 1.3 microns.

The slurries were mixed with PMDA/4,4′ODA polyamic acid solution (20.6%polyamic acid solids, approximately 50 Poise viscosity), in amounts toyield 7 wt % carbon black and 30 wt % barium sulfate on a cured filmbasis. The mixture was finished by incrementally adding a 6 wt %solution of PMDA in DMAC, with mixing, to achieve a final viscosity of2400 Poise. The finished polymer mixture was vacuum degassed. Thepolymer mixture was cast onto Mylar® polyethylene terephthalate sheetand chemically imidized and cured as described in Example 3.

Results are shown in table 1.

Examples 6-7 demonstrates lower amount of matting agent still achieveslow 60 degree gloss value (matte appearance) on both sides of base filmas well as high dielectric strength with chemical conversion.

Example 6

A chemically imidized black polyimide base film was prepared as inExample 1, except that the metering rate of silica slurry was reduced by37%. Based on ash analysis the base film contained 2.2 wt % silica.

Results are shown in table 1.

Example 7

Carbon black and silica slurries were prepared as in Example 1. APMDA/4,4′ODA prepolymer solution (20.6% polyamic acid solids,approximately 50 Poise viscosity) was “finished” by mixing in a highshear mixer with a 5.8 wt % PMDA solution in DMAC, in order to increasemolecular weight and viscosity to approximately 2500 Poise. A meteredstream of the finished polyamic acid solution was cooled toapproximately −10° C. Similarly cooled metered streams of conversionchemicals acetic anhydride (0.18 cm3/cm3 polymer solution) and3-picoline (0.17 cm3/cm3 polymer solution), along with metered streamsof carbon black (0.095 cm3/cm3 polymer solution) and silica slurries(0.029 cm3/cm3 polymer solution), were mixed with a high shear mixerinto the polyamic acid solution. The cooled mixture was filtered andimmediately cast into a film, using a slot die, onto a 105° C. hot,rotating drum. The resulting gel film was stripped off the drum and fedinto a tenter oven, where it was dried and cured to a solids levelgreater than 98%, using convective and radiant heating. The base filmcontained approximately 5.5 wt % carbon black. Based on ash analysis thefilm contained 1.8 wt % silica.

Results are shown in table 1.

Example 8

A carbon black slurry was prepared as in Example 1. An alumina slurrywas prepared as in Comparative Example 3. The slurries were mixed withPMDA/4,4′ODA prepolymer solution (20.6% polyamic acid solids,approximately 50 Poise viscosity), in amounts to yield 5 wt % carbonblack and 10 wt % alumina on a cured film basis. The mixture wasfinished by incrementally adding a 6 wt % solution of PMDA in DMAC, withmixing, to achieve a final viscosity of 1900 Poise. The finished polymermixture was vacuum degassed. The polymer mixture was cast onto Mylar®polyethylene terephthalate sheet and chemically imidized and cured asdescribed in Example 3.

Results are shown in table 1.

Comparative Example 7

Comparative Example 7 demonstrates thermal conversion using the sameamount of matting agent used in example 8 produces a high (undesirable)60 degree gloss value on both sides of base film and has a lowdielectric strength.

A carbon black slurry was prepared as in Example 1. An alumina slurrywas prepared as in Comparative Example 3. The slurries were mixed withPMDA/4,4′ODA prepolymer solution (20.6% polyamic acid solids,approximately 50 Poise viscosity), in amounts to yield 5 wt % carbonblack and 10 wt % alumina on a cured film basis. The mixture wasfinished by incrementally adding a 6 wt % solution of PMDA in DMAC, withmixing, to achieve a final viscosity of 1900 Poise. The finished polymermixture was vacuum degassed. A film was cast and thermally imidized asdescribed in Comparative Example 2.

Results are shown in table 1.

Comparative Examples 8 and 9 demonstrate amount of matting agent above1.5 weight % was needed to achieve low 60 degree gloss value (matteappearance) on both sides of the base film.

Comparative Example 8

The base film was prepared as in example 3 with 1 wt % silica on a curedfilm basis.

Results are shown in table 1.

Comparative Example 9

The base film was prepared as in example 3 with 1.5 wt % silica on acured film basis.

Results are shown in table 1.

Comparative Examples 10 and 11 demonstrate that there is a lower limitto the matting agent median particle size to achieve low 60 degree glossvalue.

Comparative Example 10

A carbon black slurry was prepared as in Example 1. An alumina slurrywas prepared, consisting of 81.4 wt % DMAC, 8.3 wt %PMDA/BPDA/4,4′-ODA/PPD prepolymer solution (14.5 wt % polyamic acidsolids in DMAC), 0.1 wt % of a dispersing agent and 10.2 wt % fumedalumina powder. The ingredients were thoroughly mixed in a rotor stator,high-speed dispersion mill. The slurry was then milled in a media millto break down large agglomerates and achieve a median particle size ofabout 0.35 μm. The slurries were mixed with PMDA/4,4′ODA prepolymersolution (20.6% polyamic acid solids, approximately 50 Poise viscosity),in amounts to yield 5 wt % carbon black and 2 wt % alumina on a curedfilm basis. The mixture was finished by incrementally adding a 6 wt %solution of PMDA in DMAC, with mixing, to achieve a final viscosity of2150 Poise. The finished polymer mixture was vacuum degassed. Thepolymer mixture was cast onto Mylar® polyethylene terephthalate sheetand chemically imidized and cured as described in Example 3.

Results are shown in table 1.

Comparative Example 11

A anhydrous dicalcium phosphate (CaHPO4) slurry was prepared, consistingof 11.5 wt % dicalcium phosphate, 64.7 wt % polyamic acid prepolymersolution (20.6 wt % polyamic acid solids in DMAC), and 23.8 wt % DMAC.The ingredients were thoroughly mixed in a high shear rotor-stator typemixer. Median particle size was 1.25 microns.

The dicalcium phosphate slurry was metered into and mixed with a cooled(−8° C.) metered stream of the finished polymer/carbon black mixture ofExample 1, along with the conversion chemicals, and a polyimide film wascast and cured using essentially the same process as Example 1. Theresulting base film contained 5 wt % carbon black and 2.8 wt % dicalciumphosphate.

Results are shown in table 1.

Comparative Example 12

Comparative Example 12 demonstrates a high density matting agent willproduce a high (undesirable) 60 degree gloss value on both sides of basefilm.

A carbon black slurry was prepared as in Example 1. A barium titanate(Sakai, BT-05) slurry was prepared, consisting of 75 wt % DMAC, 10 wt %polyamic acid prepolymer solution (20.6 wt % polyamic acid solids inDMAC), and 15 wt % barium titanate powder. The ingredients werethoroughly mixed in a high shear rotor-stator type mixer and thensonicated to achieve a median particle size of 1.5 microns.

The slurries were mixed with PMDA/4,4′ODA prepolymer solution (20.6%polyamic acid solids, approximately 50 Poise viscosity), in amounts toyield 5 wt % carbon black and 2 wt % barium titanate on a cured filmbasis. The mixture was finished by incrementally adding a 6 wt %solution of PMDA in DMAC, with mixing, to achieve a final viscosity of1500 Poise. The finished polymer mixture was vacuum degassed. Thepolymer mixture was cast onto Mylar® polyethylene terephthalate sheetand chemically imidized and cured as described in Example 3.

Results are shown in table 1.

Examples 9, 10 and 11

The base films were prepared as in Example 3, except the amount ofsilica slurry was adjusted to yield 5 wt %, 7.5 wt %, and 10 wt % silicarespectively on a cured film basis.

Results are shown in table 1.

Examples 12 and 13

The films were prepared as in Example 1. The slurries were mixed withPMDA/4,4′ODA prepolymer solution (20.6% polyamic acid solids,approximately 50 Poise viscosity), in amounts to yield 5 wt % carbonblack and 2.2 wt % silica on a cured film basis. The mixture wasfinished, cast into film, chemically imidized, and cured as described inExample 1. Conditions were adjusted to produce 2 mil and 5 mil thickbase films.

Results are shown in table 1.

Examples 14 and 15

Silica powder (Syloid® C 803) was processed in an air classifier inorder to remove a portion of the largest particles. A slurry wasprepared from the air classified silica as described in Example 1.Median particle size was 2.1 microns. A carbon black slurry was preparedas in Example 1. The carbon black and silica slurries were mixed withPMDA/4,4′ODA prepolymer solution (20.6% polyamic acid solids,approximately 50 Poise viscosity), in amounts to yield 5 wt % carbonblack and 2 wt % and 4 wt % silica on a cured film basis. The mixtureswere finished and the base film was prepared as in Example 3.

Results are shown in table 1.

Example 16

Example 16 demonstrates that chemical conversion using a different lowconductivity carbon black still achieves low 60 degree gloss value(matte appearance) on both sides of base film as well as high dielectricstrength.

A carbon black slurry was prepared, consisting of 80 wt % DMAC, 10 wt %prepolymer solution (20.6 wt % polyamic acid solids in DMAC), and 10 wt% channel-type carbon black with 6% volatiles content (Printex U, fromEvonik Degussa). The ingredients were thoroughly mixed in a rotor statordisperser. The slurry was then processed with an ultrasonic processor(Sonics & Materials, Inc., Model VCX-500) in order to deagglomerate thecarbon black. Silica slurry was prepared as in Example 1. The slurrieswere mixed with PMDA/4,4′ODA prepolymer solution (20.6% polyamic acidsolids, approximately 50 Poise viscosity), in amounts to yield 5 wt %carbon black and 2 wt % silica on a cured film basis. The mixture wasfinished by incrementally adding a 6 wt % solution of PMDA in DMAC, withmixing, to achieve a final viscosity of 2250 Poise.

The procedure described in Example 3 was used to prepare the chemicallyimidized base film.

Results are shown in table 1.

Comparative Example 13

Comparative Example 13 demonstrates thermal conversion with the sameamount of matting agent as in Example 16, produces a high (undesirable)60 degree gloss value on both sides of base film and low dielectricstrength.

The slurries were prepared as in Example 16. The finished polymermixture was manually cast onto a glass plate using a stainless steelcasting rod. The glass plate containing the wet cast film was placed ona hot plate at 80-100° C. for 30-45 minutes to form a partially dried,partially imidized “green” film. The green film was peeled from theglass and placed on a pin frame. The pin frame containing the green filmwas placed in a 120° C. oven. The oven temperature was ramped to 320° C.over a period of 60-75 minutes, held at 320° C. for 10 minutes, thentransferred to a 400° C. oven and held for 5 minutes, then removed fromthe oven and allowed to cool.

Results are shown in table 1.

Example 17

Example 17 demonstrates that chemical conversion using a different lowconductivity carbon black still achieves low 60 degree gloss value(matte appearance) on both sides of base film as well as high dielectricstrength.

The base film was prepared as in example 16 except that the carbon blackslurry was prepared from a furnace black with 3.5% volatiles content(Special Black 550, from Evonik Degussa).

Results are shown in table 1.

Comparative Example 14

Comparative Example 14 demonstrates thermal conversion with the sameamount of matting agent as in example 17, produces a high (undesirable)60 degree gloss value on both sides of base film and low dielectricstrength.

The base film was prepared as in comparative example 13 except that thecarbon black slurry was prepared from a furnace black with 3.5%volatiles content (Special Black 550, from Evonik Degussa).

Results are shown in table 1.

Example 18

Example 18 demonstrates that chemical conversion using a different lowconductivity carbon black still achieves low 60 degree gloss value(matte appearance) on both sides of base film as well as high dielectricstrength.

The base film was prepared as in example 16 except that the carbon blackslurry was prepared from a furnace black with 1.2% volatiles content(Printex 55, from Evonik Degussa).

Results are shown in table 1.

Comparative Example 15

Comparative Example 15 demonstrates thermal conversion with the sameamount of matting agent as in example 18, produces a high (undesirable)60 degree gloss value on both sides of base film and low dielectricstrength.

The base film was prepared as in Comparative Example 13 except that thecarbon black slurry was prepared from a furnace black with 1.2%volatiles content (Printex 55, from Evonik Degussa).

Results are shown in table 1.

Comparative Example 16

Comparative Example 16 demonstrates that desirable 60 degree gloss valueon the air side of the base film can be achieved with thermal conversionby using a high loading (30 weight %) of matting agent, but the otherside of the base film has high (undesirable) 60 degree gloss value andthat the dielectric strength is low.

Carbon black and silica slurries were prepared as in Example 1. Theslurries were mixed with PMDA/4,4′ODA prepolymer solution (20.6%polyamic acid solids, approximately 4500 Poise viscosity), in amounts toyield 5 wt % carbon black and 30 wt % silica on a cured film basis. Themixture was adjusted to a viscosity of 300 Poise by incrementally addinga 6 wt % solution of PMDA in DMAC, with mixing. The finished polymermixture was vacuum degassed. Using a stainless steel casting rod, a filmwas manually cast onto a glass plate. The glass plate containing the wetcast film was placed on a hot plate at 80-100° C. for 30-45 minutes toform a partially dried, partially imidized “green” film. The green filmwas peeled from the glass and placed on a pin frame. The pin framecontaining the green film was placed in a 120° C. oven. The oventemperature was ramped to 320° C. over a period of 60-75 minutes, heldat 320° C. for 10 minutes, then transferred to a 400° C. oven and heldfor 5 minutes, then removed from the oven and allowed to cool.

Results are shown in table 1.

TABLE 1 Air wt % low matting side other Air side conductivity wt %matting agent agent 60 side 60 surface Dielectric carbon matting D50Density degree degree resistivity strength Thickness Thickness Conv.black agent (microns) g/cc gloss gloss (ohm/sq) (V/mil) (mils) (microns)O.D.  1 chemical 5% SB4 3.5% 2.0 2.1 12.5 12.3 1.32E+15 2664 0.60 15.204.31 silica  2 chemical 5% SB4 7% 2.3? 3.9 22.4 26.0 1.11E+15 3102 0.5814.7 3.64 alumina  3 chemical 5% SB4 2% silica 2.0 2.1 27.0 31.29.30E+14 2668 0.74 18.8 4.88  4 chemical 5% SB4 3% silica 2.0 2.1 15.918.7 1.60E+15 1951 1.11 28.2 5.86  5 chemical 7% SB4 10% 1.3 4.4 17.425.2 1.69E+15 1411 1.40 35.60 6.02 BaSO4 c1 thermal 7% SB4 10% 1.3 4.470.4 91.1 <500 0.63 16 5.85 BaSO4 c2 thermal 5% SB4 4% silica 2.0 2.171.3 76.0 8.97E+14 <500 1.06 26.9 5.75 c3 thermal 7% SB4 30% 2.3 3.927.6 61.3 1.14E+16 1403 0.49 12.4 4.31 alumina c4 chemical 7% SB4 — 83.794.0 2394 1.35 34.3 6.09 c5 chemical 7% SB4 — — 113.7 112.1 8.43E+142968 0.52 13.2 4.78 c6 chemical 7% SB4 30% 1.3 4.4 3.3 5.0 8.57E+14 8131.34 34 6.09 BaSO4  6 chemical 5% SB4 2.2% 2.0 2.1 23.5 23.8 8.19E+152790 0.55 14 4.14 silica  7 chemical 5.5% SB4 1.8% 2.0 2.1 25.6 26.81.34E+15 2728 0.6 15.20 4.32 silica  8 chemical 5% SB4 10% 2.3 3.9 19.923.4 2505 0.75 19.1 4.79 alumina c7 thermal 5% SB4 10% 2.3 3.9 75.3 87.4<500 1.42 36.1 6.07 alumina c8 chemical 5% SB4 1% silica 2.0 2.1 47.853.1 9.36E+14 2404 0.92 23.4 5.62 c9 chemical 5% SB4 1.5% 2.0 2.1 44.750.4 2776 0.67 17 4.02 silica c10 chemical 5% SB4 2% 0.35 2.0 43.3 51.82910 1.01 25.7 5.07 fumed Al2O3 c11 chemical 5% SB4 2.8% 1.25 2.9 69.168.9 1.36E+15 3131 0.52 13.2 3.41 CaHPO4 c12 chemical 5% SB4 2% 1.5 8.073.2 81.2 2737 1.03 26.2 5.97 barium titanate  9 chemical 5% SB4 5%3.3-3.6 2.1 6 10.8 5.46E+15 2130 1.23 31.2 >6 silica 10 chemical 5% SB47.5% 3.3-3.6 2.1 3.9 5.8  2.6E+16 1523 2.98 75.7 >6 silica 11 chemical5% SB4 10% 3.3-3.6 2.1 2.4 2.8 1.00E+15 1822 1.22 31.00 >6 silica 12chemical 5% SB4 2.2% 3.3-3.6 2.1 21.7 21.5 1.34E+15 2037 2.15 54.6 >6silica 13 chemical 5% SB4 2.2% 3.3-3.6 2.1 22.9 24.9 5.767E+15  1719 5127 >6 silica 14 chemical 5% SB4 2% 2.1 2.1 33.2 41.5   1E+16 2494 1.2130.7 >6 silica 15 chemical 5% SB4 4% 2.1 2.1 13.9 19.2 9.09E+15 2215 1.538.1 >6 silica 16 chemical 5% Printex U 2% 3.3-3.6 2.1 13.1 18.61.08E+15 2393 1.08 27.4 5.48 silica c13 thermal 5% Printex U 2% 3.3-3.62.1 69.1 79.6 1.27E+15 1165 0.98 24.9 4.52 silica 17 chemical 5% Special2% 3.3-3.6 2.1 11.1 12.4 8.64E+14 1525 1.43 36.3 1.78 Black 550 silicac14 thermal 5% Special 2% 3.3-3.6 2.1 56.1 55.6  6.2E+15 461 1.47 37.31.56 Black 550 silica 18 chemical 5% Printex 2% 3.3-3.6 2.1 9.8 11.06.18E+14 1594 1.44 36.6 2.13 55 silica c15 thermal 5% Printex 2% 3.3-3.62.1 45.7 45.3 1.51E+15 559 1.65 41.9 2.2 55 silica c16 thermal 5% SB430% 3.3-3.6 2.1 0.9 59.4 4.84E+13 288 0.86 21.8 5.74 silica

Note that not all of the activities described above in the generaldescription or the examples are required, that a portion of a specificactivity may not be required, and that further activities may beperformed in addition to those described. Still further, the order inwhich each of the activities are listed are not necessarily the order inwhich they must be performed. After reading this specification, theordinary artisan will be capable of determining what activities can beused for their specific needs or desires.

In the foregoing specification, the invention has been described withreference to specific embodiments. However, one of ordinary skill in theart appreciates that various modifications and changes can be madewithout departing from the scope of the invention as set forth in theclaims below. All features disclosed in this specification may bereplaced by alternative features serving the same, equivalent or similarpurpose.

Accordingly, the specification and figures are to be regarded in anillustrative rather than a restrictive sense and all such modificationsare intended to be included within the scope of the invention.

What is claimed is:
 1. A matte finish base film with a 60 degree glossvalue of from 2 to 35 comprising: A. a chemically converted polyimide inan amount from 71 to 96 weight percent of the base film, the chemicallyconverted polyimide being derived from: a. at least 50 mole percent ofan aromatic dianhydride, based upon a total dianhydride content of thepolyimide, and b. at least 50 mole percent of an aromatic diamine basedupon a total diamine content of the polyimide; B. a low conductivitycarbon black present in an amount from 2 to 9 weight percent of the basefilm; and C. a matting agent which is silica that: a. is present in anamount from 1.6 to 10 weight percent of the base film, b. has a medianparticle size from 1.3 to 10 microns, and c. has a density from 2 to 4.5g/cc.
 2. The base film in accordance with claim 1 wherein: a. thearomatic dianhydride is selected from the group consisting of:pyromellitic dianhydride, 3,3′,4,4′-biphenyl tetracarboxylicdianhydride, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride;4,4′-oxydiphthalic anhydride, 3,3′,4,4′-diphenyl sulfone tetracarboxylicdianhydride, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane, bisphenol Adianhydride, and mixtures thereof; and b. the aromatic diamine isselected from the group consisting of: 3,4′-oxydianiline,1,3-bis-(4-aminophenoxy)benzene, 4,4′-oxydianiline, 1,4-diaminobenzene,1,3-diaminobenzene, 2,2′-bis(trifluoromethyl)benzidene,4,4′-diaminobiphenyl, 4,4′-diaminodiphenyl sulfide,9,9′-bis(4-amino)fluorine and mixtures thereof.
 3. The base film inaccordance with claim 1 wherein the chemically converted polyimide isderived from pyromellitic dianhydride and 4,4′-oxydianiline.
 4. Amultilayer film comprising the base film of claim 1 and an adhesivelayer.
 5. The multilayer film in accordance with claim 4, wherein theadhesive layer is an epoxy resin selected from the group consisting of:bisphenol A epoxy resin, cresol novolac epoxy resin, phosphoruscontaining epoxy resin, and mixtures thereof.
 6. The multilayer film inaccordance with claim 4, wherein the multilayer film is a coverlay film.7. The base film in accordance with claim 1, wherein the base film has athickness from 8 to 152 microns.
 8. A chemically converted polyimidebase film with matte surfaces and a 60 degree gloss value of from 2 to35 comprising: (1) a chemically converted polyimide in an amount from 71to 96 weight percent of the base film, the chemically convertedpolyimide being derived from pyromellitic dianhydride and an aromaticdiamine; (2) a low conductivity carbon black present in an amount from 2to 9 weight percent of the base film; and (3) a silica matting agentpresent in an amount from 1.6 to 10 weight percent of the base film,wherein the matting agent has a median particle size from 1.3 to 10microns, and a density from 2 to 4.5 g/cc.
 9. The film in accordancewith claim 8, having a thickness from 10 to 40 microns.
 10. The film inaccordance with claim 9, wherein the film has a thickness from 10 to 40microns; a 60 degree gloss from 10 to 35; and an optical density greaterthan or equal to
 2. 11. The film in accordance with claim 9, wherein thefilm is bidirectionally stretched.
 12. The film in accordance with claim8, wherein the film is unidirectionally stretched.
 13. A reduced gloss,chemically converted polyimide film, comprising: (1) a chemicallyconverted polyimide being derived from pyromellitic dianhydride and anaromatic diamine, wherein, (i) the polyimide film contains a lowconductivity carbon black present in an amount from 2 to 9 weightpercent of the film with a mean particle size from 0.2 to 1 micron and avolatile content greater than or equal to 5%; (ii) the film contains asilica matting agent in an amount from 1.6 to 10 weight percent of thepolyimide film with a median particle size from 1.3 to 10 microns and adensity from 2 to 4.5 g/cc; and (2) the polyimide film has a thicknessfrom 10 to 40 microns, surfaces with a 60 degree gloss from 2 to 35; andan optical density greater than or equal to
 2. 14. A reduced gloss,polyimide film, comprising: a chemically converted polyimide film ofpyromellitic dianhydride chemically converted with an aromatic diamine,the polyimide film has surfaces with a 60 degree gloss from 2 to 35 anduniform color intensity, a thickness from 10 to 40 microns, an opticaldensity greater than or equal to 2, and contains a low conductivitycarbon black with a volatile content greater than or equal to 5%, and aninorganic silica matting agent in an amount sufficient to achieve thereduced gloss, wherein said amount of inorganic silica matting agent isat least 20 percent less than an amount of inorganic silica mattingagent required to achieve an equivalent level of reduced gloss in athermally converted polyimide film.
 15. The reduced gloss, polyimidefilm of claim 14, wherein said amount of inorganic silica matting agentis at least 30 percent less than an amount of inorganic silica mattingagent required to achieve an equivalent level of gloss in a thermallyconverted polyimide film.
 16. The reduced gloss, polyimide film of claim14, wherein said amount of inorganic silica matting agent is at least 40percent less than an amount of inorganic silica matting agent requiredto achieve an equivalent level of gloss in a thermally convertedpolyimide film.